The goat’s natural tendency to butt its head against objects (and other goats’ heads) was used to advantage in the development of these exhibits.  Once again, the trainers at ABE took advantage of a common animal behavior and placed it in a "human" situation in order to make it entertaining.  Watch the video clips to see the “strong man” goat strike the bell.  (I wonder if he's trying to impress his girlfriend?)  Further, it would be possible to use differential reinforcement to reinforce "light" head-butting or "hard" head-butting in goats.